Fig 4.

NEUROG2 blocks S phase reentry via the repression of CCND1 and CCNE. (Aa to Ac and Ca to Cd) Close-ups on transversal sections of embryos electroporated with the mentioned constructs and incubated 30 min with BrdU just before harvesting, 6 h following electroporation. GFP in green; BrdU in red. (Ad and Ce) Histograms presenting the quantification of the BrdU incorporation rate in the mentioned experimental conditions (***, P < 0.001; Student t test). (B) Schematic representation of G₁/S transition, which is controlled by two families of cyclin: CCND and CCNE. An important restriction point (R) is located at the end of G₁ phase. The passage of this point leads to nonreversible passage through S phase. Phosphorylation of pRb by CDK4/6 cyclin D leads to E2F release. E2F promotes cyclin E transcription that in turn further phosphorylates pRb releasing more E2F. High levels of E2F promote the passage through the restriction point in late G₁ and activate CCNA transcription that drives cells through S phase and replication. (D) Flow cytometry analysis of cell cycle phase distribution: representative example of the profile of cells expressing control DNA. (E) Curves showing the repartition of the cells in G₁/G₀, S, and G₂/M phases measured on FACS profiles of GFP-positive cells 6 h following electroporation with CTL, NEUROG2, CCND1, or NEUROG2 and CCND1 (*, P < 0.05; Student t test).